Field of the Disclosure
The present invention relates generally to power conversion systems, and in particular but not exclusively, relates to an interface circuit including a reference pin for use in a power conversion system.
Background
Operation of a power conversion systems is usually controlled by a controller that may be designed as an integrated circuit module with pins or terminals coupled to sense data received from inputs and outputs of the power conversion system. The controllers generate control signals for the active elements/components of the power conversion systems to regulate the output in response to the data sensed through the pins or terminals. A common example of a power conversion system may include a switched mode power converter, and can be used in a wide variety of applications such as battery chargers or household appliances.
The cost of the controllers that are used to generate control signals for the power conversion systems can vary as a function of the complexity of the control circuitry, the semiconductor area required for the internal circuits of the controller, as well as the number of pins or terminals that are utilized by the controllers. In general, as additional functions for controllers for power conversion systems are added, corresponding additional pins or terminals are added to the integrated circuit module of the controller. As a consequence, each additional function that is added to a power converter controller generally translates into an additional pin on the power converter controller chip, which translates into increased costs and additional external components. Another consequence of providing additional functionality to a power converter controller is that sometimes there is often a substantial increase in power consumption of the controller as the number of functions of the power convert controller increases.
Flexibility in defining multiple modes of operation by an end customer is an asset in power converter controller integrated circuits. Different modes of operation in some applications may include output voltage range, frequency of operation, or any other adjustable feature of the controller. Mode selection by the end customer is usually realized through selecting specific external circuitry or components coupled to a “mode define” terminal of the integrated circuit that requires adding an extra pin or terminal to the controller integrated circuit, which translates into extra cost.
In almost all analog controlled power converters, a precise reference current source is required for charging a timing capacitor in an oscillator circuit that is used for an internal clock and/or in the filter circuits included in the analog controlled power converters. A dedicated pin or terminal of the controller is usually assigned to provide precise reference trimming for a precise reference current that is utilized in all conditions of operation.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.